Apparatus and methods related to ferrite based circulators

ABSTRACT

Apparatus and methods related to ferrite based circulators are disclosed. A ferrite disk used in a circulator can be configured to reduce intermodulation distortion when routing radio-frequency signals having closely spaced frequencies. Such a reduction in intermodulation distortion can be achieved by adjusting magnetization at the edge portion of the ferrite disk. By way of an example, a ferrite disk with a reduced saturation magnetization (4PiMs) edge portion can reduce intermodulation distortion. Example configurations with such a reduced 4PiMs edge portions are disclosed.

RELATED APPLICATIONS

This application is a continuation application of U.S. application Ser.No. 13/463,394, filed May 3, 2012, which is a non-provisional of andclaims priority to U.S. Provisional Application No. 61/483,595, filed onMay 6, 2011, entitled “APPARATUS AND METHODOLOGIES RELATED TO FERRITEBASED CIRCULATORS,” which is hereby incorporated herein by reference inits entirety.

BACKGROUND

Field

The present disclosure generally relates to circulators, and, moreparticularly to ferrite-based circulators configured to reduceintermodulation distortion.

Description of the Related Art

A circulator is a radio-frequency (RF) device typically having three orfour ports, where RF power entering one port is routed to another port.When an RF signal is being routed between two selected ports, it can bedesirable to isolate other port(s) from such a signal. Accordingly, acirculator is sometimes also referred to as an isolator. In RFapplications, circulators are typically used to route to-transmit andreceived signals to and from an antenna. Such signals can involvedifferent frequencies; and thus, intermodulation distortion can arise.

SUMMARY

In accordance with a number of implementations, the present disclosurerelates to a passive circulator having a ferrite plate that extendslaterally and having a perimeter to define a center portion and an edgeportion. The center portion has a first saturation magnetization valueand the edge portion having a second saturation magnetization value thatis less than the first saturation magnetization value. The passivecirculator further includes a magnet assembly disposed relative to theferrite plate to provide a static magnetic field to the ferrite plate tomagnetize the ferrite plate, with the magnetization configured tofacilitate transmission of a radio-frequency signal between first andsecond locations along the perimeter of the ferrite plate based on astanding wave pattern formed in the ferrite plate due to themagnetization. The passive circulator further includes first and secondelectrical conductors disposed relative to the first and secondlocations to facilitate the transmission of the radio-frequency signalbetween the first and second locations.

In some embodiments, the circulator can further include a magneticcircuit for the magnet assembly, with the magnetic circuit configured toprovide a return path for the magnetic field.

In a number of embodiments, the circulator can further include an innerflux conductor disposed relative to the ferrite disk and configured toprovide resonator and matching network functionalities.

According to some embodiments, the circulator can further include adielectric structure disposed along and outside of the perimeter, withthe dielectric structure configured to facilitate impedance matchingbetween the first and second electrical conductors.

According to a number of embodiments, the perimeter of the ferrite diskcan have a shape such as a circular shape or a triangular shape.

Some embodiments of the passive circulator can be configured whereferrite disk is formed as a single piece disk, or includes a first piecehaving the first saturation magnetization value and a second piecehaving the second saturation magnetization value. In some of such latterconfigurations, the second piece of the ferrite disk can form a ringabout the second piece.

According to a number of implementations, the present disclosure relatesto a method for reducing intermodulation distortion. The method includesproviding a ferrite medium having a first saturation magnetization toallow passage of a transmit signal between first and second locations ofthe ferrite medium and passage of a receive signal between the secondand a third location of the ferrite medium. The method further includesproviding an edge portion of the ferrite medium with a second saturationmagnetization that is lower than the first saturation magnetization toreduce intermodulation distortion occurring at the edge portion of theferrite medium.

In some implementations, the reduced intermodulation distortion caninclude a reduction of a third order product of fundamentals of thetransmit and receive signals to a level of at least about −85 dBc. Sucha reduction of the third order product can be to a level of at leastabout −90 dBc.

In various embodiments, the present disclosure relates to a passivecirculator module for isolating transmit and receive RF signals fromeach other. The module includes a ferrite disk having a center and anedge, and having a first saturation magnetization value between thecenter and a first radius that is between the center and the edge and asecond saturation magnetization value between the first radius and theedge. The module further includes a magnet assembly configured toprovide a static magnetic field to the ferrite disk to magnetize theferrite disk. The module further includes signal ports coupled to thetransmit RF signal, the receive RF signal, and an antenna.

In some embodiments, the module can further include a housing configuredto contain the ferrite disk, the magnet assembly, and at least a portionof the signal ports.

In some embodiments, the module can further include a dielectric ringdisposed along the outside of the edge of the ferrite disk. Such aferrite disk can be formed as a single piece disk.

In some embodiments, the module can further include a circular diskhaving the first radius and a circular ring having an inner diametergreater than or equal to the first radius and an outer diameter at theedge of the ferrite disk.

In accordance with a number of embodiments, the present disclosurerelates to a passive ferrite based isolator for isolating transmit andreceive wireless signals from each other when sharing a common antenna.The isolator has a reduced intermodulation distortion of a third orderproduct of fundamentals of the transmit and receive signals at a levelof at least about −85 dBc.

In some implementations, the present disclosure relates to a wirelessdevice having a transmitter circuit, a receiver circuit, and an antennaconfigured to transmit signals from the transmitter circuit and toreceive signals for the receiver circuit. The wireless device furtherincludes a ferrite based circulator for isolating transmit and receivesignals between the transmitter and receiver circuits. The circulatorincludes a ferrite disk having a center and an edge, and having a firstsaturation magnetization value between the center and a first radiusthat is between the center and the edge and a second saturationmagnetization value between the first radius and the edge. Thecirculator further includes a magnet assembly configured to provide astatic magnetic field to the ferrite disk to magnetize the ferrite disk.The circulator further includes signal ports coupled to the transmittercircuit, the receiver circuit, and the antenna.

In some embodiments, the wireless device can include a mobile telephone.

In some implementations, the present disclosure relates to a diskassembly for a radio-frequency circulator. The disk assembly includes aferrite disk having a first saturation magnetization value. The diskassembly further includes a first piece dimensioned to form a perimeteraround the ferrite disk, and has a second saturation magnetization valuethat is less than the first saturation magnetization value. The diskassembly further includes a second piece dimensioned to form a perimeteraround the second piece. The second piece includes a desired dielectricmaterial. The ferrite disk and the first and second pieces areconfigured to provide desired magnetization at or near an edge portionof the disk assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically depict examples of 3-port and 4-portcirculators.

FIGS. 2A and 2B show examples of magnetic fields that can be applied tothe example circulators of FIGS. 1A and 1B to achieve desired routingfunctionalities.

FIG. 3 shows an example circulator having a pair of ferrite disksdisposed about an inner conductor and between a pair of magnets.

FIG. 4 shows an example of significant radial component in magnetizationthat can exist at or near the edge portion of the example circulator ofFIG. 3.

FIG. 5 shows that interactions of intermodulation signals in circulatorscan occur primarily at the edge portion of ferrite disks.

FIG. 6 shows a process that can be implemented to control magnetizationof a ferrite device to reduce intermodulation distortion (IMD).

FIG. 7 shows an example process that can be implemented in the contextof a circular disk shaped ferrite as a more specific example of theprocess of FIG. 6.

FIG. 8 shows another example process that can be implemented as a morespecific example of the process of FIG. 6, where one or more structurescan be positioned at or near the radial edge of the ferrite disk toobtain a desired magnetization.

FIG. 9 shows an example configuration that can result from the processof FIG. 8.

FIG. 10 shows an example of IMDs that can result from two fundamentalfrequencies f₁ and f₂ that are relatively close to each other infrequency space.

FIG. 11 shows an example test setup for generating and measuring IMDssuch as those of FIG. 10.

FIG. 12 shows examples of IMD measurement results.

FIGS. 13A-13C show an example passive circulator device having one ormore features described herein and packaged as a modular device.

FIGS. 14A-14H show more detailed measurement results.

FIG. 15 schematically shows an example radio-frequency device where acirculator or an isolator having one or more features described hereincan be implemented.

FIGS. 16A-16C show various views of an example ferrite-based disk havingone or more features described herein, and how such a disk can beassembled.

FIG. 17 shows that in some implementations, the ferrite-based disk ofFIG. 16 can be obtained by cutting a plurality of pieces from a longerassembly.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

In some implementations, circulators are passive devices utilized inradio-frequency (RF) applications to, for example, selectively route RFsignals between an antenna, a transmitter, and a receiver. If a signalis being routed between the transmitter and the antenna, the receiverpreferably should be isolated. Accordingly, a circulator is sometimesalso referred to as an isolator; and such an isolating performance canrepresent the performance of the circulator.

In some embodiments, a circulator can be a passive device having threeor more ports (e.g., ports for antenna, transmitter and receiver). FIGS.1A and 1B schematically show an example of a 3-port circulator 100 and a4-port circulator 104. In the example 3-port circulator 100, a signal isshown to be routed (arrow 102) from port 1 to port 2; and port 3 can besubstantially isolated from such a signal. In the example 4-portcirculator 104, a signal is shown to be routed (arrow 106) from port 1to port 2; and another signal is shown to be routed (arrow 108) fromport 3 to port 4. The two junctions of the signal paths in the exampleof FIG. 1B can be substantially isolated from each other. Otherconfigurations of 3 and 4-port circulators, as well as circulatorshaving other numbers of ports, can also be implemented.

In some implementations, a circulator can be based on ferrite materials.Ferrites are magnetic materials having very high ohmic resistance.Accordingly, ferrites have little or no eddy current when subjected tochanging magnetic fields, and are therefore suitable for RFapplications.

Ferrites can include Weiss domains, where each domain has a net non-zeromagnetization. When there is no external magnetic field influencing aferrite object, the Weiss domains are oriented substantially randomly,so that the ferrite as a whole has a net magnetization of approximatelyzero.

If an external magnetic field of sufficient strength is applied to theferrite object, the Weiss domains tend to align along the direction ofthe external magnetic field. Such a net magnetization can influence howan electromagnetic wave propagates within the ferrite object.

For example, and as depicted in FIGS. 2A and 2B, suppose that a circulardisk shaped ferrite object 110 is subjected to a substantially staticexternal magnetic field directed along the axis (perpendicular to theplane of paper) of the disk. In the absence of such an external field(not shown), an RF signal input into Port 1 and propagatingperpendicular to the disk axis splits into two rotating waves with asubstantially same propagation speed. One wave rotates clockwise aroundthe disk, and the other counter-clockwise around the disk, so as toyield a standing wave pattern. If Ports 2 and 3 are positioned equallyspaced azimuthally relative to Port 1 (about 120 degrees from eachother), the standing wave pattern results in approximately half of theincoming wave leaving each of Ports 2 and 3.

In the presence of such an external magnetic field, the propagationspeeds of the two rotating waves are no longer the same. Because of thedifference in the propagation speeds, the resulting standing wavepattern can yield a situation where substantially all of the energy ofthe incoming wave is passed to one of the two ports while the other portis substantially isolated.

For example, FIG. 2A shows a configuration where the axial staticmagnetic field (not shown) yielding a rotated standing wave patternrelative to the incoming wave propagation direction (along Port 1).Examples of electric field lines corresponding to such a standing wavepattern are depicted as 112 (along a plane of the disk) and 114, 116(along the axis of the disk). The example rotated standing wave patternresults in a substantial null in electric field strength at Port 3,thereby yielding substantial isolation of Port 3. On the other hand,Port 2 is depicted as having a similar (inverted) wave pattern as thatof the input at Port 1, and therefore transmits energy from Port 1 toPort 2.

FIG. 2B shows another example where an axial static magnetic field (notshown) yields a rotated standing wave pattern, such that a wave inputthrough Port 1 is passed to Port 3 as an output, and Port 2 issubstantially isolated. In some implementations, the two rotatedstanding wave patterns can be achieved by providing magnetic fields thatare higher and lower than a field value that results in a resonance inthe precession of ferrite domains.

FIG. 3 shows an example configuration of a circulator device 130 havinga pair of ferrite disks 132, 134 disposed between a pair of cylindricalmagnets 142, 144. The magnets 142, 144 can be arranged so as to yieldgenerally axial field lines through the ferrite disks 132, 134. Themagnetic field flux that passes through the ferrite disks 132, 134 cancomplete its circuit (depicted by arrows) through return paths providedby 148, 152, 150 and 146 so as to strengthen the field applied to theferrite disks 132, 134. In some embodiments, the return path portions148 and 146 can be disks having a diameter larger than that of themagnets 142, 144; and the return path portions 152 and 150 can be hollowcylinders having an inner diameter that generally matches the diameterof the return path disks 148, 146. The foregoing parts of the returnpath can be formed as a single piece or be an assembly of a plurality ofpieces.

The example circulator device 130 can further include an inner fluxconductor 140 disposed between the two ferrite disks 132, 134. Such aninner conductor can be configured to function as a resonator andmatching networks to the ports (not shown).

The example circulator device 130 can further include a high relativedielectric (Er) material 136, 138 disposed between the edge portion ofthe ferrite disks 132, 134 and the return path portions 150, 152. Such ahigh Er dielectric can be formed as a ring dimensioned to fit betweenthe corresponding ferrite disk and the outer return path portion.

In some implementations, such a dielectric ring can be part of acomposite ferrite/dielectric TM resonator, where the dielectric replacessome of the ferrite. A high dielectric constant material can be used tokeep the diameter of the composite approximately the same as aferrite-only resonator at a desired frequency. In some embodiments, sucha dielectric material can have a dielectric constant value between about16 and 30, but are not necessarily confined to that range. For example,a dielectric constant value as high as about 50 can also be utilized. Insome implementations, such a dielectric can provide a non-magnetic gapbetween the ferrite and the return path magnetic field to therebyimprove the IMD reduction performance over a configuration where theferrite extends further out to the return path.

Non-limiting examples of materials that can be utilized for the variousparts of the foregoing example circulator device 130 are describedherein in greater detail.

As described herein (e.g., in reference to FIGS. 2A and 2B), adisk-based circulator generally has an intrinsically symmetrical RFfield distribution in the ferrite disk. The static magnetic field,however, can change considerably at the edge portion of the ferritedisk. FIG. 4 shows such an example, where magnetization vectordirections are shown for a ferrite disk subjected to a substantiallyuniform static magnetic field in the axial direction. As seen in theaxial view (along the Z direction), the vector directions at or near theedge portion have significant radial components.

It has been reported that interactions of intermodulation signals incirculators occur primarily at the edge of the disks. Such an effect isdepicted in FIG. 5, where a rectangular loop represents a couplingbetween an RF field and magnetization for an intermodulation of signalsassociated with an input (port 1) and an output (port 2). Moreparticularly, such a coupling can contribute to a third orderintermodulation product having a frequency 2ω₁−ω₂, where ω₁ and ω₂ arethe frequencies of the input and output signals, respectively.

In some situations, and as described herein in reference to FIG. 3, astatic magnetic field can be distorted by the shape of the magnet and/orthe presence of a magnetic return path in the circulator. In the exampleof FIG. 4, the deviation of magnetization vector directions away fromthe axial direction along the edge portion can be due to such adistortion.

In some situations, such a distortion can influence how well saturatedthe edge of a ferrite is, and hence its susceptibility to nonlinearbehavior in the presence of RF fields. For example, a reduced axialfield at or near the ferrite's edge portion can result in the ferrite todrop back towards the resonance absorption peak, thereby increasing theinsertion loss. At low microwave frequencies relative to the ferrite'ssaturation magnetization (also referred to as 4πMs or 4PiMs), low fieldloss is also possible even above resonance.

In some situations, the foregoing nonlinear behavior can result inintermodulation distortion (IMD) resulting from two or more signalsmixing within a device to produce undesirable higher-order products.These unwanted higher-order signals can fall within transmitting orreceiving bands and cause interference (also referred to asintermodulation distortion).

Accordingly, in some implementations, it is desirable to control themagnetization of a ferrite based device so as to reduce the amount ofIMD. FIG. 6 shows a process 180 that can be implemented to achieve sucha feature. In block 182, a ferrite material can be provided. In block184, the ferrite material and/or its surrounding can be configured toyield a desired magnetization of the ferrite material when subjected toa static magnetic field.

For the purpose of description herein, a circular disk shaped ferritematerial is utilized to demonstrate various features of the disclosure.It will be understood, however, that one or more features of the presentdisclosure can also be implemented in other shaped ferrites, including,for example, a non-circular slab such as a triangular shaped slab, aswell as other non-slab shaped objects.

In the context of a circular disk shaped ferrite, a process 190 of FIG.7 can be a more specific example of the process 180 of FIG. 6. In block192, a ferrite disk can be provided. In block 194, one or more surfacesof the ferrite disk can be treated to obtain a desired magnetizationwhen subjected to a static magnetic field. An example of such a surfacetreatment is described herein in greater detail.

In another example, a process 200 of FIG. 8 can be implemented, where inblock 202, a ferrite disk can be provided. In block 204, one or morestructures can be disposed at or near the radial edge of the ferritedisk to obtain a desired magnetization when subjected to a staticmagnetic field. An example of such a structure is described herein ingreater detail.

FIG. 9 shows that in some implementations, a circulator device 210 canbe configured to have one or more features that can yield a desiredmagnetization of one or more ferrite disks 212, 214. One or more of theferrite disks 212, 214 can have one or more surfaces treated so as toyield or contribute to the desired magnetization.

In the circulator device 210, a pair of cylindrical magnets 252, 254 isshown to provide a static magnetic field for magnetization of theferrite disks 212, 214. The magnetic field flux that passes through theferrite disks 212, 214 can complete its circuit (depicted by arrows)through return paths provided by 264, 274, 272 and 262 so as tostrengthen the field applied to the ferrite disks 212, 214. In someembodiments, the return path portions 264 and 262 can be disks having adiameter larger than that of the magnets 252, 254; and the return pathportions 274 and 272 can be hollow cylinders having an inner diameterthat generally matches the diameter of the return path disks 264, 262.The foregoing parts of the return path can be formed as a single pieceor be an assembly of a plurality of pieces.

The example circulator device 210 can further include an inner fluxconductor 240 disposed between the two ferrite disks 212, 214. Such aninner conductor can be configured to function as a resonator andmatching networks to the ports (not shown).

The example circulator device 210 can also include a high relativedielectric (Er) material 232, 234 disposed between the edge portion ofthe ferrite disks 212, 214 and the return path portions 272, 274. Suchhigh Er dielectric material 232, 234 can be formed as a ring dimensionedto fit within the inner walls of the outer return path portions 272,274.

In some implementations, the example circulator device 210 can includestructures 222, 224 disposed at or near the edge portions of the ferritedisks 212, 214. In the example shown, each of the structures 222, 224can be a ring dimensioned to fit between the high Er dielectric ring(232 or 234) and the outer edge of the ferrite disk (212 or 214).

In some implementations, each of the rings 222, 224 can be formed from amaterial having a lower saturation magnetization (4PiMs) than that ofthe ferrite disk (212 or 214). Combined, each of the ferrite disk andthe lower-4PiMs ring can yield a magnetizable disk having a reduced4PiMs at the edge portion. As described herein, such a combination canyield a reduction in the IMD of the circulator device 210.

Table 1 lists some non-limiting examples of materials or features thatcan be utilized for the various parts of the circulator 210 described inreference to FIGS. 3 and 9.

TABLE 1 Part(s) Example Material(s) and/or Feature(s) Magnets (142, 144Permanent magnets having field strength in FIG. 3; 252, sufficient toyield saturation magnetization of 254 in FIG. 9) ferrite disks whenassembled. Return path (148, 152, Steel, which is preferable when RFsignals 150, 146 in FIG. 3; 264, cause large eddy currents in goodconductors 274, 272, 262 in FIG. 9) such as soft iron. Inner conductor(140 in High RF conductivity metal such as copper, FIG. 3; 240 in FIG.9) brass, silver etc. Ferrite disks Yttrium iron garnet (YIG) having a4PiMs of (132, 134 in FIG. 3; about 1780 Gauss (referred to as “G113”212, 214 in FIG. 9) herein) or any 4PiMs greater than the ferrite rings232, 234 High Er dielectric rings Referred to as “D30” herein.Dielectric (136, 138 in FIG. 3; constant value can be between about 16and 232, 234 in FIG. 9) 30, or can be higher up to about 50.Reduced-4PiMs rings Garnet such as YIG with a low 4PiMs of about (232,234 in FIG. 9) 1000 Gauss (referred to as “G1010” or “G- 1210” herein)or any 4PiMs significantly lower than the ferrite disks 212, 214.

It will be understood that a number of other types of materials andmaterials having different values or properties can also be used toimplement one or more features of the present disclosure.

In the example described in reference to FIG. 9 and Table 1, the reduced4PiMs at the edge portion of a ferrite disk can be provided by anaddition of a ring having a lower 4PiMs value. Such a ring configurationcan be an example where the ferrite disk and the ferrite ring form aferrite assembly formed from separate pieces. In some embodiments, asingle-piece ferrite structure (e.g., a disk) can also be used, wherethe single-piece structure has two or more regions having different4PiMs values. For example, a center portion of a disk can have a first4PiMs value, and an edge portion can have a second 4PiMs value that islower than the first value.

To demonstrate improvements in IMD isolation performance associated withone or more features of the present disclosure, Applicant measured thirdorder products resulting from two closely spaced (in frequency) RFsignals. An example of such an IMD is depicted in FIG. 10, where twofundamental frequencies f₁ and f₂ are relatively close to each other infrequency space. Odd-numbered products form relatively close to thefundamentals; and among such odd-numbered products, the third-orderproducts are typically the most dominant, and thus of greatest concern.Such third-order products occur at frequencies centered at about 2f₁−f₂and 2f₂−f₁.

Such IMDs can be formed and measured in a number of ways. FIG. 11 showsan example test setup 300 where various configurations of a circulator302 can be tested. Two signal generators can generate two fundamentalsignals having closely spaced frequencies (f₁ and f₂). Each signal canbe conditioned (e.g., amplifier, dual isolator, and low-pass filter asshown), then combined and fed into the circulator 302. An output signalcan be conditioned (e.g., attenuator and notch filter as shown) andmeasured by, for example, a spectrum analyzer.

FIG. 12 shows examples of results obtained from the foregoinginvestigation of the localization of the IMD effect. The vertical scaledenotes amplitude in dBc. The values of the various bars showncorrespond to average values of upper third-order peak amplitudes.

The right-most bar (“G-113 Straight Ferrite”) is for a configurationsimilar to that of FIG. 3 without the dielectric rings (136, 138).Moving to the left, the bar indicated as “G-113/G-1210 Assembly” is fora configuration where a reduced 4PiMs ring (G-1210) is provided on theoutside of the ferrite (G-113). The bar indicated as “G-113/G-1210/D30Triple Assay” is for a configuration where both of the reduced 4PiMsring (G-1210) and the dielectric ring (D30) are provided on the outsideof the ferrite (G-113) (e.g., similar to FIG. 9). The bar indicated as“G-113/D30 Assembly” is for a configuration the dielectric ring (D30) isprovided on the outside of the ferrite (G-113), but not G-1210 (e.g.,similar to FIG. 3). The left-most bar indicated as “System IM” isrepresentative of a detection limit of the measurement system, and canbe considered to be a theoretical situation where no IMD contributioncomes from the circulator/isolator.

Experiments utilizing the foregoing circulator configurations theexample setup of FIG. 11 were performed at about 400 MHz and at about900 MHz, with the fundamentals being separated by about 5 MHz. Theresults depicted in FIG. 12 are for the 900 MHz experiment; andfollowing observations can be made. The presence of the lowmagnetization ring (in the G-113/G-1210/D30 configuration) resulted inan IMD reduction of about −92 dBc, which is an improvement of about 5 dBin IMD isolation when compared to the configuration without the lowmagnetization ring (G-113/D30) (about −87 dBc). Without the lowmagnetization ring, the presence of the dielectric ring (G-113/D30)performs better than the configuration without the dielectric ring(G-112) (about −82 dBc). Without the dielectric ring, the presence ofthe low magnetization ring (G-113/G-1210) appears to make very littleimprovement over the configuration without the low magnetization ring(G-113).

Relative to the “System IM” result (at about −97 dBc), theG-113/G-1210/D30 configuration (about −92 dBc) shows the best resultsamong the configurations tested. When compared to the worst of theexample configurations (G-113 at about −82 dBc), the improvement ofabout 10 dB can be realized. In some implementations, an improvement ofabout 20 dB or more can also be achieved.

In some implementations, a passive circulator device having one or morefeatures can be packaged as a modular device. An example of such adevice is shown in FIGS. 13A-13C. A circulator module 500 can include acirculator 510 packaged in a housing 502. Such a housing 502 can beconfigured to facilitate mounting of the module 500, via, for example,mounting holes 504. The example circulator 510 of the module 500 is a3-port circulator; and RF signals to and/or from the circulator 510 canbe passed through electrical contacts 512, 514, 516. Various dimensionsof the example circulator module 500 are listed in Table 2.

TABLE 2 Dimension reference Approximate dimension D1  25.4 mm D2  25.4mm D3  20.8 mm D4  20.8 mm D5  2.3 mm D6  2.3 mm D7  7.6 mm D8  0.6 mmD9  12.7 mm D10 9.0 mm (max) D11 3.8 mm D12 2.8 mm D13 3.0 mm D14 1.3 mm

For the purpose of description, the example single junction circulatormodule 500 described in reference to FIG. 13 and Table 2 is referred toas a SKYFR-000700 module. In some embodiments, the compact dimension(about 25 mm×25 mm) module 500 can be designed to operate in the GSMband of 925 MHz-960 MHz. As described herein, some configurations of theSKYFR-000700 module can achieve IMD performance of better than about −90dBc with two CW tones of +47 dBm, spaced 5 MHz apart.

For the purpose of demonstrating such an improved IMD performance, theSKYFR-000700 module was configured with a circulator having a tripleassembly similar to the configuration described herein asG-113/G-1210/D30 and having G-113 ferrite disks, reduced magnetizationrings G-1210, and dielectric rings D30. For comparison, a circulatordevice (referred to as MFR000xxx herein) was configured with acirculator having a configuration similar to that of G113/D30 describedherein.

The foregoing circulator modules SKYFR-000700 and MFR000xxx were testedin a setup similar to the setup described in reference to FIG. 11 undertwo frequency conditions. The first test condition was as follows:F1=925 MHz, +47 dBm, CW tone; F2=930 MHz, +47 dBm, CW tone. The secondtest condition was as follows: F1=955 MHz, +47 dBm, CW tone; F2=960 MHz,+47 dBm, CW tone.

Table 3 shows examples of results obtained from the foregoing IMDmeasurements.

TABLE 3 Approx. Approx. Frequency IMD Module (MHz) (dBc) See Figure(s)MAFR-000xxx 925 −73 FIG. 14A: MAFR-000xxx at 925 MHz MAFR-000xxx 960 −73FIG. 14B: MAFR-000xxx at 955 MHz SKYFR-000700 925 −92 FIG. 14C:SKYFR-000700 at 925 MHz FIG. 14D: SKYFR-000700, close up of third orderproduct at 935 MHz FIG. 14E: SKYFR-000700, close up of third orderproduct at 920 MHz SKYFR-000700 960 −91 FIG. 14F: SKYFR-000700 at 955MHz FIG. 14G: SKYFR-000700, close up of third order product at 950 MHzFIG. 14H: SKYFR-000700, close up of third order product at 965 MHzAs one can see, IMD performance improvements of the SKYFR-000700circulator module over the MAFR-000xxx device is more than 10 dB at allof the tested frequencies.

In the context of the carrier wave power as a reference, a circulatorhaving one or more features of the present disclosure can be configuredto provide a third-order IMD level of at least approximately −85 dBc,−86 dBc, −87 dBc, −88 dBc, −89 dBc, −90 dBc, −91 dBc, −92 dBc, −93 dBc,−94 dBc, −95 dBc, −96 dBc, or −97 dBc.

As described herein, one or more features of the present disclosure canbe utilized to achieve improved IMD performance in the example GSM band.Such one or more features can also be utilized to achieve similarimprovements in IMD performance in other GSM bands, other cellular band,and/or other non-cellular frequency ranges.

FIG. 15 shows that in some embodiments, one or more circulators orisolators described herein can be implemented in a radio-frequency (RF)device 600. The example RF device 600 can include a transceiver 604having a transmitter 606 and a receiver 608. The transmitter 606 can beconfigured to generate an RF signal based on signals received from abaseband sub-system 602. The RF signal generated by the transmitter 606is shown to be amplified by a power amplifier (PA) 610; and theamplified RF signal is shown to be sent to an antenna 614.

In the example RF device 600, the antenna 614 is shown to receive anincoming RF signal; and the received signal is routed to an low-noiseamplifier (LNA) 612. The amplified received signal is then sent to thereceiver 608 for processing; and the processed signal can be passed onto the baseband sub-system 602.

In the foregoing path between the transmitter 606 and the PA 610, anisolator 210 can be provided to isolate the to-be-amplified RF signal asit goes from port 1 to port 2. Such an isolation can be achieved byconnecting port 3 to an appropriately configured termination path.

Similarly, in the foregoing path between the LNA 612 and the receiver608, an isolator 210 can be provided to isolate the LNA-amplified signalas it goes from port 2 to port 1. Such an isolation can be achieved byconnecting port 3 to an appropriately configured termination path.

In the foregoing example where the antenna 614 is shared for bothtransmit and receive operations, routing of the amplified signal (fromthe PA 610) and the received signal (to the LNA 612) can be facilitatedby a circulator 210 as shown. In the example, port 2 is shown to beconnected to the PA 610, port 2 is shown to be connected to the antenna614, and port 3 is shown to be connected to the LNA 612. Thus, theamplified signal from the PA 610 enters port 1 of the circulator 210 andexits at port 2 to be routed to the antenna 614. The received signalfrom the antenna 614 enters port 2 of the circulator 210 and exits atport 3 to be routed to the LNA 612.

In some implementations, at least some of the isolators and/or thecirculator of FIG. 15 can include one or more features as describedherein to reduce IMD distortions. In some embodiments, the examplecirculator 210 can benefit especially due to the same device handlingboth transmit and receive signals thereby creating a conditionsusceptible to IMDs.

In some embodiments, the RF device 600 can include a wireless device.Such a wireless device can include a portable device, or a deviceconfigured for stationary systems such as a base station.

FIGS. 16A-16C show various views of an example ferrite-based disk havingone or more features described herein, and how such a disk can beassembled. In an assembled form (FIGS. 16A and 16B), an exampleferrite-based disk 700 is shown to include a ferrite center piece 212which is surrounded by a ring 222 having a lower 4PiMs value than thatof the ferrite center 212. The reduced 4PiMs ring 222 is shown to besurrounded by a dielectric ring 232. The disk 700 can be one of the twodisks (212, 222, 232; and 214, 224, 234) described in reference to FIG.9.

FIG. 16B shows that when assembled, the ferrite center 212 and thereduced 4PiMs ring 222 form a joint 702. Similarly, the reduced 4PiMsring 222 and the dielectric ring 232 form a joint 704. Depending on howthe pieces are assembled, such joints can be formed by, for example, anadhesive, shrink-fitting one part around another, and/or press-fitting.

FIG. 16C shows that the unassembled pieces 212, 222, 232 can bedimensioned appropriately to accommodate one or more assemblytechniques. The ferrite center piece 212 is shown to have an overalldiameter of d1. The reduced 4PiMs ring is shown to have an innerdiameter of d2 and an outer diameter of d3. The dielectric ring is shownto have an inner diameter of d4 and an outer diameter of d5.

By way of examples, if the ferrite center piece 212 and the reduced4PiMs ring 222 are to be press-fitted, then both can be sinteredappropriately to yield desired physical properties and shrinkage, andthen machined so that the dimensions d1 and d2 allow press-fitting. Inanother example, if the same pieces are to be assembled by an adhesive,the dimensions d1 and d2 can be selected to accommodate such anadhesive.

In yet another example, suppose that the dielectric ring 232 is to beshrunk-fit around an assembly of the reduced 4PiMs ring and the ferritecenter (e.g., press-fit together with pre-shrunk pieces). The innerdiameter dimension d4 of the dielectric ring 232 in its unfiredcondition can be selected to be larger than the outer diameter d3 of thereduced 4PiMs ring 222 in its fired condition, to allow the outer ringto slip over the inner ring. Then, firing of the assembly can shrink theouter ring (232) over the inner ring (222). Additional detailsconcerning such “co-firing” methods can be found in U.S. Pat. No.7,687,014, titled “CO-FIRING OF MAGNETIC AND DIELECTRIC MATERIALS FORFABRICATING COMPOSITE ASSEMBLIES FOR CIRCULATORS AND ISOLATORS,” whichis hereby incorporated herein by reference in its entirety.

FIG. 17 shows that in some implementations, the ferrite-based disk 700of FIG. 16 can be obtained by first assembling longer pieces to yield alonger assembly 710. Then, a plurality of disks 700 can be cut from thelonger assembly 710. Such cutting can be achieved in a number of knownways, and the cut disks 700 can be finished to yield, for example,desired finish and/or dimensions.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While certain embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A passive circulator, comprising: a pair offerrite plates, a center portion of each of the ferrite plates having afirst saturation magnetization value and an edge portion of each of theferrite plates having a second saturation magnetization value that islower than the first saturation magnetization value; a pair ofdielectric structures, each dielectric structure disposed along an outerperimeter of one of the ferrite plates; a pair of magnets that provide astatic magnetic field to the ferrite plates to magnetize the ferriteplates, the ferrite plates disposed between the pair of magnets; and ahousing that surrounds and encloses the pair of magnets, the pair offerrite plates and the pair of dielectric structures, and which providesa return path for the magnetic field, the dielectric structuresextending laterally from said outer perimeter of the ferrite plates toan inner surface of the housing.
 2. The circulator of claim 1 furthercomprising an inner flux conductor disposed between the pair of ferriteplates and configured to provide resonator and matching networkfunctionalities.
 3. The circulator of claim 1 wherein a perimeter ofeach of the ferrite plates has a circular shape.
 4. The circulator ofclaim 1 wherein a perimeter of each of the ferrite plates has atriangular shape.
 5. The circulator of claim 1 wherein each of theferrite plates is formed as a single piece disk.
 6. The circulator ofclaim 1 further comprising first and second electrical conductorsdisposed relative to first and second locations so as to facilitate thetransmission of the radio-frequency signal between the first and secondlocations.
 7. The circulator of claim 6 wherein the pair of dielectricstructures are configured to facilitate impedance matching between thefirst and second electrical conductors.
 8. The circulator of claim 1wherein each of the ferrite plates is a ferrite disk that includes afirst piece having the first saturation magnetization value and a secondpiece having the second saturation magnetization value.
 9. Thecirculator of claim 8 wherein the second piece of the ferrite disk formsa ring about the first piece.
 10. A passive circulator module forisolating transmit and receive radio-frequency signals from each other,the module comprising: a pair of ferrite plates each defining a centerportion and an edge portion, the center portion having a firstsaturation magnetization value and the edge portion having a secondsaturation magnetization value that is less than the first saturationmagnetization value; a pair of dielectric rings, each dielectric ringdisposed along an outer perimeter of the edge portion of one of theferrite plates; a pair of magnets that provide a static magnetic fieldto the ferrite plates to magnetize the ferrite plates, the ferriteplates disposed between the pair of magnets; a housing that surroundsand encloses the pair of magnets, the pair of ferrite plates and thepair of dielectric rings, and which provides a return path for themagnetic field, the dielectric rings extending laterally from said edgeportions of the ferrite plates to an inner surface of the housing; andsignal ports coupled to a transmit radio-frequency signal, a receiveradio-frequency signal, and an antenna.
 11. The module of claim 10wherein the housing comprises a plurality of separate pieces.
 12. Themodule of claim 10 wherein each of the ferrite plates is formed as asingle piece disk.
 13. The module of claim 10 wherein each of theferrite plates includes a circular disk having a first radius thatdefines the center portion, and a circular ring that defines the edgeportion, the circular ring having an inner diameter greater than orequal to the first radius and an outer diameter at an outer edge of theferrite plate.
 14. A wireless device, comprising: a transmitter circuit;a receiver circuit; an antenna configured to transmit signals from thetransmitter circuit and to receive signals for the receiver circuit; anda passive circulator for isolating transmit and receive signals betweenthe transmitter and receiver circuits, including (a) a pair of ferriteplates each defining a center portion having a first saturationmagnetization value and an edge portion having a second saturationmagnetization value that is lower than the first saturationmagnetization value; (b) a pair of dielectric structures, eachdielectric structure disposed along an outer perimeter of one of theferrite plates; (c) a pair of magnets that provide a static magneticfield to the ferrite plates to magnetize the ferrite plates, the ferriteplates disposed between the pair of magnets; (d) a housing thatsurrounds and encloses the pair of magnets, the pair of ferrite platesand the pair of dielectric structures, and which provides a return pathfor the magnetic field, the dielectric structures extending laterallyfrom said outer perimeter of the ferrite plates to an inner surface ofthe housing; and (e) signal ports coupled to the transmitter circuit,the receiver circuit, and the antenna.
 15. The wireless device of claim14 wherein the wireless device includes a base station.
 16. A method forreducing intermodulation distortion, the method comprising: providing apair of ferrite plates having a ferrite medium, the ferrite plateshaving a center portion with a first saturation magnetization to allowpassage of a transmit signal between first and second locations of theferrite medium and passage of a receive signal between the second and athird location of the ferrite medium, the pair of ferrite plates havingan edge portion with a second saturation magnetization that is lowerthan the first saturation magnetization to reduce intermodulationdistortion occurring at the edge portion of the ferrite plates;disposing a pair of dielectric structures along an outer perimeter ofthe ferrite plates; applying a static magnetic field to the pair offerrite plates with a pair of magnets, the pair of ferrite platesdisposed between the pair of magnets; and providing a return path forthe magnetic field with a housing that surrounds and encloses the pairof ferrite plates, the pair of dielectric structures and the pair ofmagnets, the dielectric structures extending laterally from said outerperimeter of the ferrite plates to an inner surface of the housing. 17.The method of claim 16 wherein the second saturation magnetization ofthe edge portion reduces a third order product of fundamentals of thetransmit and receive signals to a level of at least about −85 dBc. 18.The method of claim 17 wherein the reduction of the third order productis to a level of at least about −90 dBc.